E. A. Lavrinovich

Speciation of radionuclides in colloidal matter of underground waters taken from observation wells in the zone of impact of Lake Karachai

Associations of radionuclides with colloidal particles of various sizes, isolated from underground waters of the Lake Karachai contamination area, were studied. Analysis by photon correlation spectroscopy showed that the total content of colloidal matter in deeper horizons is higher by an order of magnitude than in near-surface horizons. The mean particle radius also increases with the depth. The major fraction of Pu, Am, and Cm is associated with colloids (40–90%). U and Np are associated with colloidal particles to a lesser extent (2–20%), which determines their higher migration mobility in underground waters. The amount of actinides associated with coarse colloidal particles of size from 450 to 200 nm is insignificant. A considerable fraction of actinides is in the deep-lying water (depth ≥40 m) is associated with colloidal particles of size from 200 to 50 nm. No more than 30% of Pu and Am in water of these horizons is associated with finer colloids (from 10 kDa to 50 nm). With approaching the surface, the amount of actinides in the fraction of nanometer-sized particles (50 nm-10 kDa) increases (to 50%).

Luminescence analysis of underground waters of the Lake Karachai contamination area for the neptunium content and forms of occurrence

A luminescence procedure using crystal phosphors was developed for Np determination in environmental objects. The procedure allows the sensitivity of the Np determination to be increased by an order of magnitude relative to traditional α-ray spectrometric analysis. A specialized photometer developed for this purpose is described. The attained Np detection limit in natural waters is 0.1–0.8 Bq l−1. With membrane preconcentration, the detection limit can be decreased to 3 × 10−4 Bq l−1. The procedure was successfully tested in monitoring of groundwaters of the Lake Karachai contamination area.

Membrane luminescence determination of technogenic actinides and their speciation in environmental objects

Researchers of the Vernadsky Institute of Geochemistry and Analytical Chemistry of the Russian Academy of Sciences created a luminescence photometer of a new generation for the determination of trace amounts of uranium and transuranium elements (TUE). The limits of detection for actinides vary from 0.3 pg for uranium and neptunium to 2.0 pg for plutonium. For 237Np, the relative limit of detection is 0.008 Bq/L. The photometer was tested in the radioecological monitoring of a number of polluted zones in Russia. The dynamics of actinide migration in all of the studied zones enhanced in the series 239Pu < 241Am < 237Np. In this series, concentrations of radionuclides in water-soluble and exchange forms that are most mobile and determine the migration mobility of chemical elements increased in all of the studied soil types. In the group of fulvic acids, concentrations of radionuclides decreased in the series 237Np > 241Am > 239Pu irrespectively of the soil. In the group of humic acids, concentrations of radionuclides increased in the series 237Np < 239Pu < 241Am. The sorption coefficients of radionuclides by bottom sediments of the Markha River (Kraton-3 underground nuclear explosion site) and Lake Kyzyltash (East Urals Radioactive Trace) were calculated. Bioaccumulation factors of radionuclides by different plants in the impact area of the Kraton underground nuclear explosion were determined depending on the plant type.

Neptunium speciation in soils

The relative content of 237Np in the water-soluble form depends on the soil type and decreases in the following order: sandy loam soil > soddy podzolic soil > chernozem (black soil). The fraction of the most mobile forms of 237Np decreases with an increase in the content of organic carbon in soils. The major fraction of 237Np is associated with the fulvic acid (FA) group (90.3 and 71.0% of the total neptunium content for soddy podzolic soil and chernozem, respectively), with 8.6 and 18.7% of 237Np, respectively, associated with the humic acid (HA) group. In the FA group, the major fraction of 237Np is associated with low-molecular-weight organic compounds and with FA, free or bonded mainly with relatively mobile hydroxides of Fe, Al, Mn, etc. (R2O3·nH2O) (fractions 1a and 1).

Luminescence determination of trace neptunium in natural waters with the separation of iron as a quencher

A method is proposed for the luminescence determination of neptunium in natural waters with the removal of interfering iron. For the separation of iron ionic and colloidal species, solid-phase extraction with N-benzoyl-phenylhydroxylamine as a complexing reagent is used. The method makes possible the reduction of iron concentration in samples by more than two orders of magnitude without noticeable losses of neptunium and, therefore, the attainment of a detection limit for neptunium equal to its value in samples containing no iron.

Model for Pu Migration in Soils

The term migration is understood as the movements of chemical elements in environmental components. One of the major tasks of radioecology is the elucidation of migration patterns and reliable long term prediction of the behavior of radionuclides in the environment. The migration mechanisms of radionuclides practically do no differ from those of any other chemical elements, and hence, the direction, intensity, and mechanisms of the migration of radionuclides are controlled, first of all, by their speciation and residence times in ecosys tems and by the natural conditions in these systems. It should be mentioned that the mobility of certain radio nuclides is greater than that of the corresponding stable isotopes and elements analogues [1, 2], because these radionuclides come to the environment in the form of more mobile species [3].

Contents of radionuclides in soil and biota at the site of the Kraton-3 accidental underground nuclear test, Yakutia

The paper presents results of radiocological monitoring at the site of the Kraton-3 accidental underground nuclear test in Yakutia. The distribution and migration of 137Cs, 90Sr, 237Np, and 238–240Pu in the soil and its living cover of the northern taiga are analyzed, and it is demonstrated that the radioecological conditions at the territory are still adverse in spite of the rehabilitation measures.